Aggregate demand can be defined as the amount of total spending on domestic goods and services in an economy. It is a concept similar to "regular" demand (the demand for a specific good or service in a specific market), but also different from it in important ways. Which of the following is one way in which aggregate demand is different from "regular" demand? a. Aggregate demand is strongly influenced by government policy, unlike regular demand which cannot be influenced by government policy b. Aggregate demand is not affected by consumers' choices about what to buy, it remains the same as long as consumers spend the same total amount of money c. Aggregate demand cannot shift, unlike regular demand which does shift under certain circumstances d. Aggregate demand is an upward sloping curve, unlike single-market demand which is downward sloping